Multipath-aware joint symbol timing and CFO estimation in multiuser OFDM/OQAM systems

In this paper we consider the problem of data-aided synchronization in the up-link of a multiple access (MA) orthogonal frequency division multiplexing (OFDM) system based on offset quadrature amplitude modulation (OQAM). In particular, the joint maximum-likelihood (ML) phase offset, carrier-frequency offset (CFO) and symbol timing (ST) estimator, exploiting a short known preamble embedded in the burst received from each of U users in multipath channel, is considered. Under the assumption that the CFO of each user is sufficiently small, the considered approach leads to U different approximate ML (AML) estimators; moreover, delays, amplitudes and phase-offsets are jointly estimated for each path. Specifically, the phase, amplitude and CFO estimators are in closed form while the AML ST estimators require a one-dimensional maximization procedure. The performance of the proposed joint AML estimator is assessed via computer simulations both in AWGN and multipath channel.